The object of the invention includes aspects of communication networks, switching technology and Internet technologies.
Certainly the most important current field of development in the field of networks is the transmission of real-time traffic, e.g. of voice and video information, over packet-oriented networks and the provision of the known services or service features from the classical telephone networks—also referred to as PSTN (Public Switched Telephone Network) networks or TDM (Time Division Multiplexing) networks, e.g. IP (Internet Protocol) network.
One important service is the playing of recorded announcements which are played in particular situations (e.g. ‘this number is unavailable’, ‘the telephone number has changed, the new telephone number is 722-25940’, queuing announcements or missed call announcements.) In the classic case in which the payload channel of the connection is routed into the exchange these recorded announcements can be provided by devices of the exchange equipped with the corresponding functionality or can also be provided via devices external to the exchange connected via TDM/PCM technology. If however the payload data is routed outside the exchange in a packet network an external system is preferably used for this purpose. This system possesses interfaces to the packet network for the payload data consisting of recorded announcements. Further the external announcement system has a logical control interface to the exchange undertaking the control of connections routed outside the exchange in the packet network. The recorded announcement functionality of the external system is controlled by the exchange for example by means of the Media Gateway Control protocol, abbreviated to MGCP. The recorded announcement function can be in an own network element or integrated into a network element which is present for other reasons, e.g. a media gateway.
Since certain announcements are used very frequently, these are made available in a cost effective manner in TDM-based exchanges by employing broadcast functionality. Voice announcements generated are distributed via the switching matrix present in a TDM-based exchange to a plurality of subscribers. Through timed through-switching in the peripheral device even breaking into a current announcement can be suppressed, so that the subscriber has the impression that an individual announcement is being played to them from the start.
In packet-based networks a functionality which corresponds to broadcasting which reduces the costs of recorded announcement technology is not available to the same extent. The reasons for this is that multicast routing is not available from end to end under the real-time requirements of call processing execution sequences as well as the corresponding signaling standards in the packet-based networks, inadequate availability of support for this signaling in the controlling exchange—which is referred to below to distinguish it from exchanges of the classical telephony network as a packet-based exchange, very short hold times of standard announcements, problematic control of breaking in at the correct time at the start of the announcement in the end point and difficulties relating to the standard conformity to RTP/RTCP (RTP: real time protocol; RTCP: real time control protocol) in IP-based networks. The result of this is that mass recorded announcements, for reasons of simplicity and reliability, have to be operated as individual announcements. However the cost effectiveness known from TDM-IP-based networks still has to be achieved.
A further problem lies in the need to play what are known as individual announcements in which a part of the announcement is determined dynamically. (Examples of this are announcing a changed telephone number or the speaking clock.) These types of recorded announcements consist of a sequence of speech fragments which are played as a concatenated sequence in accordance with certain predefined rules and depending on the individual content and the national language required.
To optimize the transmission bandwidth a series of very different encoding methods (e.g. G.711, G.726, G.728, G.729/GA, G723.1 and G.723) are further supported for the language in packet based networks. The hardware/software devices and functions supporting these encoding methods are referred to in technical literature as codecs (coder/decoder). Depending on the capabilities of the endpoints of a connection the codec to be used or the encoding method to be used is selected according to priority standpoints within the context of the connection setup (codec negotiation is referred to in this context). If a recorded announcement machine is the endpoint of a connection it should where possible support all the encoding methods preferred by the endpoints or terminals and thereby be able to provide its announcements in all codings required by or preferred by the end points in parallel and for individual connections.